In modern internal combustion engines, such as those used to power automobiles, the mass flow rate of air entering the engine is commonly determined by a mass-air-flow (MAF) sensor. The MAF sensor is designed to respond to the amount of air flowing through a chamber containing the sensor, and is generally intended to be insensitive to the density of the flow of air being measured. Typically, MAF sensors do not measure the mass of air flow directly.
A commonly used type of an MAF sensor employs a hot wire. Such a hot wire MAF sensor measures a frequency response of the heated wire and the temperature of the air flowing past the sensor. The frequency response of the hot wire and temperature of the air flow are communicated to the engine control unit, which permits the control unit to accurately determine the mass flow rate of air entering the subject engine.
The engine control unit uses the mass air flow determined by the MAF sensor to balance and deliver the correct fuel mass to the combustion chamber(s) of the engine. Besides being used to control the engine's internal combustion process, the mass of air flow determined by the MAF sensor may also be employed to control other vehicle systems that are affected by the engine's combustion.